The present invention relates to a method of making a Schottky barrier field effect transistor, and particularly for making such a field effect transistor with a narrow gate using an insulating layer to passivate the transistor and to define the gate.
Schottky barrier field effect transistors generally comprise a body of a semiconductor material having on a surface thereof spaced source and drain contacts and a gate between the source and drain contacts. The source and drain contacts have ohmic contact with the semiconductor body and the gate has a Schottky barrier contact with the semiconductor body. These transistors are generally made by first coating the surface of the semiconductor body with a layer of a metal having an ohmic contact with the semiconductor material. Then, using a photoresist masking layer, the metal is defined by etching portions away to form the source and drain contacts. The photoresist layer is removed and a second photoresist layer is applied and photolithographically defined to provide openings for the gate. A metal layer is then deposited, generally by the technique of evaporation in a vacuum, over the photoresist layer and the surface of the semiconductor body exposed between gate openings in the photoresist layer. The photoresist layer is then removed which also lifts off the portions of the metal layer on the photoresist layer. This leaves the gate metal which then can be annealed to insure a Schottky barrier junction. An insulating layer is then coated over the device to passivate the source, drain and gate.
This method of making Schottky barrier field effect transistors has several disadvantages. This method requires several photoresist coatings and definitions, each of which takes time and adds to the cost of making the transistor. Also, each photoresist layer leaves behind some contamination which adversely affects the good adhesion of the passivation layer to the transistor. In addition, when the second photoresist layer is removed lifting off part of the metal layer, the portion of the metal layer so removed is torn or broken away from the remaining gate portion of the metal layer. This tearing away is not always clean so that the edges of the gate region are often torn or uneven.